A social insurance number (SIN) is a number issued in Canada to administer various government programs. The SIN was created in 1964 to serve as a client account number in the administration of the Canada Pension Plan and Canada's varied employment insurance programs. In 1967, Revenue Canada (now the Canada Revenue Agency) started using the SIN for tax reporting purposes. SINs are issued by Human Resources and Social Development Canada (previously Human Resources Development Canada).

The SIN is formatted as three groups of three digits (e.g., 123-456-789).

Functionality

Through functionality creep, the SIN has become a national identification number, in much the same way that the Social Security Number has in the United States. However, unlike in the US, in Canada there are specific legislated purposes for which a SIN can be requested. Unless an organization can demonstrate that the reason they are requesting a person's SIN is specifically permitted by law, or that no alternative identifiers would suffice to complete the transaction, they cannot deny or refuse a product or service on the grounds of a refusal to provide a SIN. Examples of organizations that legitimately require a SIN include employers, banks and investment companies, and federal government agencies. Giving a SIN when applying for consumer credit, such as buying a car or electronics, or allowing it to be used as a general purpose identification number, such as by your cable company, is strongly discouraged.

The Canadian military used the SIN as a form of unique identifier from the 1960s until the 1980s, when service numbers were reintroduced. Military identification, including ID cards and identity discs were marked with the SIN during this period.

Organization

Social Insurance Numbers that begin with the number "9" are issued to temporary residents who are not Canadian citizens or permanent residents (e.g., foreign students, individuals on work visas). These individuals must have an employment authorization in order to work in Canada. SINs beginning with a "9" are different from SINs assigned to citizens and permanent residents, because they have an expiry date (which usually coincides with the expiration of the holder's work authorization). These SINs are invalid unless there is an expiry date listed on the card and the date has not passed.

Validation

Canada Revenue Agency

To validate a Social Insurance Number, it is necessary to complete the following process, as outlined by the Canada Revenue Agency.

Example SIN: 046 454 286

Use the ninth digit as the check digit, while multiplying the second, fourth, sixth, and eighth digits each by two. In this case 6 is the check digit, while 4, 4, 4, and 8 all get multiplied.

4 • 2 = 8; 4 • 2 = 8; 4 • 2 = 8; 8 • 2 = 16

Add all the digits in the result of these four multiplications.

{8, 8, 8, 16} = [8 + 8 + 8 + 1 + 6] = 31

Add the first, third, fifth, and seventh digits all together.

[0 + 6 + 5 + 2] = 13

Add the results from steps two and three together.

31 + 13 = 44

If this number is a multiple of ten (ending in zero), then the check digit in step one should be a zero; otherwise subtract the total (44) from the next highest multiple of ten (50).

50 - 44 = 6

This is your check digit, or the ninth digit of the SIN.

Luhn Algorithm

While unofficial, Social Insurance Numbers can also be validated through a simple check digit process called the Luhn Algorithm.

Notice that, in the second-to-last column, 8 • 2 = 16. In the case of a two-digit number, simply add the digits together 1 + 6 and insert the result (in this case, 7). When writing a program to complete this task, (x=-9) might be simpler to implement.